My expectation was for him to immediately flip me over his shoulder, toss me on the bed, and join me in some epic sex. Instead, he just smiled at me and said, “Sorry, I’m not in the mood.”

There’s nothing quite as shocking as a man who turns down sex. Certainly for the woman — I responded to my then-boyfriend’s rejection by throwing a Gothic iron candelabra at his head — but it can be especially devastating for guys.

What does it mean when his libido disappears? Does it make him less of a man if he can’t keep up with his girlfriend sexually? And how can he get his sex drive back?

Here’s what you can do when you feel like saying, “Not tonight, dear, I have a headache.”

First — don’t freak out

Low libido in men is not uncommon. In fact, about 1 in 4 men (28%) surveyed in a 2012 study in the International Society for Sexual Medicine reported a low sexual desire.

One of the study’s authors, Dr. Irwin Goldstein, director of sexual medicine at Alvarado Hospital in San Diego, also claims “nearly 30% of women say they’re more interested in sex than their male partner.”

If you’re disinterested in sex only rarely or occasionally, there isn’t cause for concern.

Marianne Brandon, Ph.D., a clinical psychologist and sex therapist, points out that for a man’s libido to be technically diagnosed as low, he’d need to “have few sexual thoughts, fantasies, and little desire for sex for at least six months.”

De-stress

Stress is the single most powerful biological inhibitor of the sex drive, according to Nan Wise, Ph.D., a cognitive neuroscientist and certified sex therapist.

Wise suggests that men shouldn’t “power through the stress,” but take on physical activities that are more social, relaxing, and less competitive.

“Even simple things like breathing exercises or taking a hike with a guy friend can really make a difference,” she says.

“There are dozens of antidepressants with different side effects, and some affect libido more than others,” says Gail Wyatt, Ph.D., a professor of psychiatry and director of the UCLA Sexual Health Program at the Semel Institute for Neuroscience and Human Behavior. “You need to really work with your doctor.”

Redefine masculinity

Men are often socialized to be the strong one, the breadwinner, the problem solver, and the sexual dynamo. When those things are lacking, it can have an emasculating effect.

In fact, job loss is the top cause of a decreased libido among his male clientele, says sex therapist Chris Donaghue, Ph.D.

“Competition is killing sex,” says Wyatt. “When you feel less of a man, you’re not as interested in sex. It’s time to redefine what makes you a man, and learn to be happier with less.”

Take the pressure off

Masculinity does not have to be defined by how hard your penis gets, how many times a day/week you want it or how long you last.

And the culprit for those damaging ideas? You guessed it: our old friend porn.

“When guys are exposed to porn, they think they should be rock hard really fast and last really long, and that’s just a myth and unfair,” says Brandon. “They get anxious about it, and then they lose an erection, and the next time they just avoid sex altogether.”

Tease yourself

Sometimes revving up your sex drive is like revving up your car engine — you might need to press down on the gas a few times before it starts up.

“I advise my clients who want a stronger sex drive to masturbate, but not to orgasm, a few times a day, or watch a little porn, but don’t touch himself,” says Brandon. “This will trigger your body to want sex and get the body more primed and wanting.”

Ring that bell

ShutterstockJust because you have a hottie of a wife standing in front of you in sexy lingerie, sex can still become boring after a while.

“I encourage men to fantasize more, and think about how they can bring elements of that into the bedroom with their partner to make sex more interesting,” says Brandon.

It’s up to both partners to constantly introduce new and exciting layers to their sex life, to avoid “recipe sex,” says Wyatt. “You can’t keep doing the same thing, the same way, with the same person.”

Kiss and hug it out

One way to get back to that loving feeling is to simply kiss (with tongue) your partner for an uninterrupted 30 seconds, and give her a 20-second full body hug.

“The kiss stirs up the oxytocin — the cuddle hormone — which makes you bond to that person and want to be with them,” says Bonnie Eaker Weil, Ph.D., author of “Make Up, Don’t Break Up.” “It’s a powerful hormone. And, with the 20-second hug — chest-to-chest — you will feel a rush almost like when you have a drink of wine.”

Just do it

Nike had a solid point here. Even if you don’t 100% feel up to it, just do it.

“But, remember, ‘do it’ doesn’t have to mean intercourse,” says Wise. “Just be intimate. Set up time to play. It doesn’t matter if you get a hard-on or have penetration or have an orgasm. Just play and let go of the goal, and that will let go of the pressure.”